An antenna device generally has a T-shaped antenna (feed antenna) that is provided on a ground plate, and parasitic elements which are arranged on both sides of the T-shaped antenna and are short-circuited to the ground plate through a switch. Then, the switch is short-circuited or opened, and thereby variability of directivity of the antenna device is achieved.
However, when an antenna device having a large number of antennas represented by an array antenna intends to have directivity, switches become necessary which correspond to just the number of antennas, and there is a problem that the cost increases.